Internal combustion engines, such as diesel engines, are connected with exhaust systems that typically include aftertreatment systems to reduce emissions of pollutants from the tailpipe, such as NOx. Such aftertreatment systems can employ oxidation catalysts, particulate filters, and selective catalytic reduction (SCR) catalysts. Since SCR catalysts typically operate most efficiently at higher exhaust temperatures, certain exhaust heating strategies, such as hydrocarbon injection, oxidation catalysts, and/or variable geometry turbine (VGT) inlet control, are employed to increase or maintain the temperature of the SCR catalyst in its effective temperature range. However, these exhaust heating strategies and NOx emissions control with such systems are obtained at a high initial system cost, fuel penalties, and/or high operating costs over the life of the system.
SCR catalysts are subject to deterioration in performance resulting from the accumulation of various contaminants, such as sulphur and hydrocarbons, on the SCR catalyst. In exhaust systems that include particulate filters, active particulate filter regeneration can serve in part as a regeneration event for the SCR catalyst as well to remove sulphur poisoning. However, particulate filter regeneration results in a fuel penalty, and diesel particulate filters require servicing and additional expense in cost and operation of the aftertreatment system. In addition, while vanadia SCR catalysts provide improved NO conversion and tolerance to sulphur poisoning than other SCR catalysts, aftertreatment systems that employ particulate filters typically do not employ vanadia SCR catalyst due to their lack of thermal durability in high temperature conditions, such as those that occur during particulate filter regeneration.
Diesel engine exhaust systems also raise exhaust gas temperatures by controlling an opening of an inlet to a variable geometry turbine (VGT) in the exhaust system. However, VGT's are expensive and control of the opening can be complicated depending on engine operating conditions to achieve the desired result. Therefore, further technological developments are desirable in this area that provide a low cost exhaust and aftertreatment system for an internal combustion engine that are operable to meet emissions standards.